Touch enabled display screen devices are used to control numerous applications. The user communicates with the underlying application by performing various gestures. The simplest gesture is a simple touching of the screen in a predetermined location to indicate the selection of a corresponding quantity. Virtual keyboards and keypads are implemented with such gestures. Touch screen displays for controlling physical instruments present challenges due to the limited amount of space that is available for providing the controls and the need to see data that is displayed on the screen in addition to any controls. Typically, physical buttons and knobs in the prior instrument design are replaced by “widgets” that are visual displays on the screen with which the user interacts using a touch gesture of some kind. For example, a push button on the original instrument is replaced by a button widget on the touch screen which is activated by the user touching the screen at the location of the button widget.
Widgets for changing numeric values present significant challenges. Typically, a value that controls some function in the instrument must be changed in a particular manner. In some cases, the value needs to be altered in a continuous manner. For example, the amplitude or frequency of a signal generated by an instrument may require adjustment. In other cases, the value needs to be incremented or decremented in steps of a predetermined size that depend on the particular application. For example, the time scale on an oscilloscope display typically uses predetermined steps so that the ticks on the screen are at integer values.
Prior art displays often use number pads on the screen for allowing the user to input a value; however, the number pads occupy a significant fraction of the screen, and hence, interfere with the display of other information that may be needed to correctly set the desired value. Simple button widgets that increment or decrement the value in question are poorly suited to the task of changing the value in a continuous fashion.
Widgets that emulate a slider have been used for changing a value in a continuous manner; however, these widgets have limited accuracy. The ratio of the length of the slider to the size of the contact area between the user's finger and the display limit the precision with which the user can alter the value. Hence, the size of the slider needed for accurately changing a value becomes a problem when there is limited area on the display due to the need for displaying other information while adjusting the value in question.